Application Research Of Phase Change Materials In Plastic Greenhouses In South China

Greenhouses have developed rapidly in China.As of 2016,the greenhouses area has reached 2.08 million hectares.However,the winter plastic greenhouses in the south are low in temperature,which often causes the growth of vegetables to suffer from low temperature hazards.In order to improve the thermal environment of plastic greenhouses in the winter and respond to the national energy conservation and environmental protection call,this study has been based on the analysis of the current situation of southern plastic greenhouses,selected organic phase change materials suitable for plant growth for experimental and numerical simulations to explore the all-day use strategy of phase change materials in southern plastic greenhouses and the operation strategies and operational effects throughout the winter.In this study,the whole-day use strategy of phase change materials in southern plastic greenhouses was determined by the experiment of shrinking greenhouses established in the suburbs of Hangzhou to control the shed air temperature in the winter above 10? and improve the use rate of phase change materials.The packaged phase change materials are placed in the self-made heat collecting device during the day,and can be fully melted by absorbing solar energy.The placed packaged phase change materials in the experimental greenhouse at night.Through the combination of phase change materials and thermal insulation cotton,the night temperature in the shed can be maintained above 10? when the outdoor minimum temperature is-4?,and the night temperature in the shed can be maintained at 15? when the outdoor minimum temperature is 8?.Above,met the needs of chilling vegetable seeds for germination.Parallel comparison experiments have proved that the use of phase change materials can increase the temperature of the air in the night shed and reduce the temperature fluctuation in the shed.On the basis of the experiment,a numerical simulation model of the air temperature in the shed was established,and the energy balance analysis was carried out of the air in the shed.The unsteady heat conduction analysis was carried out of the components in the shed,the finite difference method was used to discretize,and phase change materials are calculated based on the equivalent specific heat capacity method.The mathematics software MATLAB was used to solve the air temperature in the shed.The air temperature in the shed simulated by the numerical calculation was compared with the temperature obtained by experiment,which verified the correctness of the numerical simulation model.Finally,according to the determined numerical simulation method,the meteorological data of Hangzhou in the typical meteorological year was selected to simulate the air temperature in the shed,and the initial conditions of the simulation were determined by the"pre-exposure method".In order to ensure the air temperature in the shed is above 10?,and the operation strategy of the phase change materials in the plastic greenhouse in Hangzhou was determined:three phase change materials modules were used in combination with 4cm thick insulation cotton.Through the calculation of thermal load and economic analysis,it can be known that the operation strategy can save 23%energy saving compared with electric heating,and the recovery period is 7 years,which is less than the service life of 10 years.This study proposed an economical and effective phase change materials operation strategy in plastic greenhouses.Sincerely hope to establish a path which can improve the thermal environment in the southern plastic greenhouse and the facility agriculture can become energy-efficient and environmentally friendly.